The goals of this project are to achieve a molecular level understanding of the biological and physiological events surrounding steroid synthesis, function and metabolism and to use this knowledge to facilitate the development of safe, effective drugs for use as steroid agonists and antagonists in controlling fertility, cancer chemotherapy, and the treatment of hypertension, atherosclerosis and other steroid hormone related disorders. X-Ray crystal structure determinations of hormonal steroids and the proteins with which they interact are being undertaken, and correlations between molecular conformation and biological activity are being elucidated. The Molecular Structure of Steroids Project has generated hundreds of steroid crystal structures in collaboration with biochemists, pharmacologists, and endocrinologists, provided answers to specific questions about steroid synthesis and activity, produced an empirical model for steroid hormone receptor binding and activity, revealed unanticipated conformations of the most potent progestins, estrogens and corticoids, and produced 164 manuscripts, 34 chapters and two volumes of the Atlas of Steroid Structures in which the structural determinations were reported and their significance discussed. The immediate goals of the project are the determination of the three- dimension structures, the mechanisms of action and inhibition and the basis for hypertension, and neoplasia (bacterial 3alpha, 20beta- hydroxysteroid dehydrogenase, 3alpha,20beta-HSD; porcine 20beta- hydroxysteroid dehydrogenase, 20beta-HSD; human 17beta-hydroxysteroid dehydrogenase, 17beta-HSD; porcine 20beta-11beta-hydroxysteroid dehydrogenase, 11beta-HSD) a microbial cholesterol esterase (Cc ChE) of relevance to atherosclerosis, and a mammalian prostatic binding protein (PBP) implicated in prostate cancer therapy. The complex of 3alpha,20beta-HSD and a licorice analogue will be used to model inhibition of mammalian 11beta-HSD and 15-hydroxy prostaglandin dehydrogenase (15-HPD). Inhibition of the former induces hypertension and of the latter combats peptic ulcers. The structure of 20beta-HSD will allow us to improve our models for the NADP-dependent 11beta-HSD and 15-HPD. The comparison of the active sites of 3alpha,20beta-HSD and 20beta-HSD should explain why 20beta-HSD does not accept corticosteroids with oxygen substituents at C(11) as substrates. The architecture of the active site revealed by X-ray analysis of 17beta-HSD will be compared with that in the observed structures of 3alpha,20beta-HSD and 20beta-HSD and the modeled structure of 11beta-HSD in order to identify features that determine 17beta specificity and might be exploited in designing active site directed inhibitors of potential use in breast cancer therapy. A comparison of the structure of Cc ChE with those of other esterases should reveal the basis for cholesterol specificity and permit design of specific inhibitors of ChE that would block hydrolysis of cholesterol esters thereby controlling cellular uptake. The structure of PBP will reveal the molecular architecture of the heterodimer and the nature of binding of estramustine and foster the design of drug-steroid conjugates that might be selectively delivered to the prostate for cancer therapy.